Good memory on the AD for the LS-87 series plugs.
Many years ago when spending time with an old "heavy" aerial applicator out here in AZ (who will remain nameless) I saw piles of the old canned LS series plugs on their parts shelves and enquired as to the massive stockpile (which I might add remained very much in use on many of their radials engines - and this was the early '80s).
The mechanic whom I queried on this grunted and acknowledged the AD and said he was aware of ceramic lining failures within the plug walls and subsequent failure and fouling on some engines, which allegedly brought about the AD after some crashes and loss of life. He didn't elaborate and I never bothered to fully research the AD history. I always suspected the ceramic coating inside the plug was somehow thinner or more prone to heat damage, but this is just pure conjecture on my part.
I do know that many of the plugs they ended up with had been military reconditioned plugs and that "recon" plugs were always the second choice versus some of the other series plugs. That, too, could have been a factor - perhaps the LS-87 was a product borne out of the recon shops? I don't know.
They referred to their stock of -87s as "ferry plugs" or "100 mile plugs" which they ran on their 2600s... and truth be told then ran 'em for more than ferry flights or short distances in spite of the reference to the nickname. They explained than at five and 10 cents per piece - which is what they'd purchased 'em for at government auctions or from the parts mongers that they were not a bad plug at all, and when they'd have a cylinder foul they'd just change a plug or 28 and away they'd go.
Of course, those fellows had bought new QEC R-2600 engines from surplus sales for $250 a whack to decades prior and changing a cylinder in the field on contract jobs was considered a lot of work... just as easy to truck in a QEC and dump a metal-maker or low-oil pressure engine in the junk pile behind the hangar...
Wonder what they'd think of $30 RHB37's today? On a side note, I've run plenty of the -87s on non-airworthy radial and V-series aero engines and they've done just fine. Many a Allison V-12 tractor pull motor used 'em as their spark source a couple of decades ago when the "fine wire" plugs were being gobbled up by the fly-boys.
My opinion on a ground display engine? Run 'em, man, run 'em. They're the best bargain to be had today for the price, and they were a military service plug in use for many years.
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